Recently, in the field of silver halide photographic materials and, particularly, with picture taking photosensitive materials, there has been a demand for photosensitive materials of extremely high sensitivity, e.g., as represented by the ISO 1600 films, which also exhibit high image quality and high sharpness and which are suitable for compact format cameras such as 110-size cameras and disk cameras.
A known means of improving the sharpness and granularity of developed images comprises incorporating in a silver halide color photographic material a compound (hereinafter referred to as a DIR compound) which releases a development inhibitor in accordance with image density at development.
Such DIR compounds are generally of the type which react with the oxidation product of an aromatic primary amine developer to release a development inhibitor. As a representative class of such compounds, there are known DIR couplers which, in their coupling position, have a group adapted to form a compound having development inhibiting activity upon cleavage from the coupling position (for example, the compounds as described in U.S. Pat. Nos. 3,227,554, 3,701,783, 4,095,984, 4,149,886, 3,933,500, 4,146,396 and 4,477,563). When such DIR couplers undergo a coupling reaction with an oxidized aromatic primary amine developing agent, the coupler nucleus forms a dye while a development inhibitor is released.
As a class of compounds which undergo a coupling reaction with an oxidized aromatic primary amine developing agent to yield a colorless coupling reaction product and, at the same time, release a development inhibitor, there are known various compounds including the compounds described in U.S. Pat. Nos. 3,632,345, 3,928,041, 3,958,993, 3,961,959 and 4,052,213 and Japanese Patent Application (OPI) Nos. 53-110529 and 54-13333 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
DIR hydroquinones, which release development inhibitors upon a cross-oxidation reaction with an oxidized developing agent, are also known. Examples of DIR hydroquinones include the compounds described in U.S. Pat. Nos. 3,379,529 and 3,930,863.
However, these compounds have the disadvantage that they suffer from a decrease in their desired function upon decomposition or undergo desensitization during storage of films containing the same after coating, and their beneficial effects on image sharpness are not very satisfactory.
A category of compounds which, on coupling with an oxidized aromatic primary amine developing agent, release a development inhibitor with a timed release effect can be exemplified by the compounds described in U.S. Pat. No. 4,248,962 and Japanese Patent Application (OPI) No. 57-56837.
It is true that, with this last type of compounds, an inhibitory effect can be realized a certain distance from a developed silver halide grain so that at least theoretically a "neighboring group" effect may enhance edge sharpness. Actually, however, as the timing of these compounds is not well controlled, they do not contribute much to the sharpness of developed images. Furthermore, as hydrolysis or cleavage inevitably occurs under high humidity storage conditions, problems such as desensitization and a decrease in their desired function are frequently encountered.
To overcome the above problems, Japanese Patent Application No. 59-33059 (corresponding to U.S. patent application Ser. No. 705,473 filed on Feb. 25, 1985 now U.S. Pat. No. 4,618,571) proposes a class of compounds where the compounds released therefrom upon a coupling reaction with one molecule of oxidized developing agent further undergo a redox reaction with another molecule of oxidized developing agent to release a photographically useful group such as a development inhibitor. This class of compounds have the general formula: EQU A-RED-PUG
where A means a coupler residue which undergoes a coupling reaction with an oxidized developing agent to release RED-PUG; RED means a group which, after cleavage from A, undergoes a redox reaction an oxidized developing agent and releases PUG; and PUG means a group which, after cleavage form RED, exhibits a substantial photographic action.
Photosensitive materials containing compounds adapted to ultimately release a development inhibitor, among the above mentioned compounds, are good in shelf life and, particularly, provide markedly improved imaged sharpness. However, when these photosensitive materials are developed, the increased fatigue of the processing solution results in changes in photographic characteristics, e.g., the development inhibiting effect is excessive under certain conditions while the reverse is true under other conditions, so that it is difficult to obtain stable effects at all times. It has also become clear that they have the serious disadvantage in that, depending on developing conditions, an uneven finish can result even within the same image frame.
The concept of using two or more different DIR compounds in silver halide photosensitive materials is disclosed, for example, in Japanese Patent Application (OPI) No. 50-119631 (corresponding to U.S. Pat. No. 4,015,988), which teaches the combined use of a DIR hydroquinone with a DIR coupler. This combination, however, has not proven sufficiently effective because of a large desensitization of the DIR hydroquinone compound.
Japanese Patent Application (OPI) No. 51-113625 teaches the simultaneous use of mercapto type development inhibitor releasing compounds having dissimilar coupling activities, but the underlying principle of this art is no more than such that the rate of release of the development inhibitor is controlled through differences in coupling activity so as to obtain satisfactory tone reproduction; the effect achieved thereby is quite different from the effect achieved by the combination of compounds according to the present invention which will hereinafter be described in detail.
Japanese Patent Application (OPI) No. 56-137353 teaches the combined use of a compound having a timing group and a compound which does not have a timing group with regard to the release of a development inhibitor, and Japanese Patent Application (OPI) No. 57-173836 teaches the combined use of a mercapto type development inhibitor releasing compound having a cleavage group and a mercapto type development inhibitor releasing compound having no such group. However, these techniques are based on the concept that two compounds having two different functions, namely a compound for providing "interimage" effects and a compound satisfying granularity requirements, are used in combination to achieve the respective effects as a mere sum of the two functions.
Japanese Patent Application (OPI) No. 56-116029 (corresponding to U.S. Pat. No. Re 31,893) teaches the combined use of a development inhibitor releasing compound having an amino group and a development inhibitor releasing compound having no amino group but it appears that this technique is also based on the concept of satisfying image quality requirements and formaldehyde resistance requirements through a mere summation of the effects of the individual compounds.
In contrast, as will be explained fully hereinafter, the effects according to the present invention are implemented by a mechanism quite different from prior art technology involving combinations of compounds.
Japanese Patent Application (OPI) No. 57-138636 describes a compound which corresponds to the compounds of the present invention minus the development inhibitor moiety, that is, a compound which releases a scavenger for oxidized developing agent. However, the compounds according to the present invention have the capability to undergo a coupling reaction with oxidized developing agent and release a development inhibitor upon reaction with another molecule of oxidized developing agent, and its effect is primarily that of development inhibition, as disclosed in Japanese Patent Application No. 59-33059, with little scavenging or cleaning out effects for oxidized developing agent. Thus, the effects are quite different from those of the above mentioned patent application.
Further, Japanese Patent Application (OPI) No. 57-155537 teaches the combined use of the above compound and a conventional DIR compound, but the purpose and rationale of such art is to utilize an oxidized developing agent scavenger releasing compound to compensate for disadvantages such as the adverse influence of the conventional development inhibitor releasing DIR compound on tone reproduction and contamination of processing solutions and, therefore, the technique of this art is quite different from the present invention in which a development inhibitor releasing compound is present in addition to a conventional DIR compound.